The major objective for this grant continues to be to characterize the properties of the first excited singlet state of molecular oxygen -02(1 delta g) - in media that resemble and model biological environments. Integral to this program are endeavors to characterize and understand the photoproperties of molecules that behave as photodynamic sensitizers and to examine the ways in which such processes depend upon the medium. The methodology used relies upon using lasers for producing pulses of light of various wavelengths for excitation of photosensitizers and subsequent generation of 02(1 delta g) of these transient entities are made using computer-controlled kinetic absorption and emission spectrophotometry with nanosecond time resolution. These allow measurements of the spectral and kinetic properties of the short- lived photo-dynamic intermediates. A new technique to be employed involves time resolved microspectrofluorimetry in individual cells. Investigative areas for the coming period include: (i) Photoproperties of tetrapyrrole (porphyrins, phthalocyanines, naphthalocyanines) and other sensitizers including examination of the effects of structure, presence of co-ordinated metal ion, aggregation state, solvent properties and medium microheterogeneity. (ii) The effects of intercalation by DNA and encapsulation with synthetic polymers and biopolymers upon the yields of sensitizer triplet state, the yields of singlet oxygen and the occurrence of Types I and II photodynamic mechanisms. (iii) A study of the efficiency with which singlet oxygen is formed during the quenching of triplet states of sensitizers. This, together vita the influence of environment on the process, will enhance our knowledge of photodynamic mechanisms. (iv) Demonstrations of the formation of singlet oxygen in cellular populations under photodynamic conditions and correlations of the yields with damage.